Wins help that's denied (8)
I believe the answer is:
gainsaid
'denied' is the definition.
(to gainsay is to deny or dispute something)
'wins help' is the wordplay.
'wins' becomes 'gains' ('gain' can be a synonym of 'win').
'help' becomes 'aid' (synonyms).
'gains'+'aid'='GAINSAID'
'that's' is the link.
(Other definitions for gainsaid that I've seen before include "Formally denied or contradicted" , "Challenged" .)